1. Field of the Invention
This invention relates to the mixing of gases and liquids. More particularly, it relates to enhancing the dispersion of gases in liquids.
2. Description of the Prior Art
The dispersion of gases in liquids is an important feature of a wide variety of industrial operations. Thus, gases are dispersed in liquids for numerous gas dissolution, gas liquid reaction and gas stripping of dissolved gas applications. As the gas is more finely dispersed in the liquid in the form of very small gas bubbles, the interfacial surface area between the gas and liquid is appreciably increased as compared to said surface area between the liquid and a like quantity of gas in the form of larger gas bubbles. In turn, an increase in the interfacial surface area between the gas and liquid is known to increase the mass transfer of the gas from the gas bubbles into the liquid, as well as the transfer of dissolved gas from the liquid into the gas bubble. Thus, by providing much higher interfacial area, all gas-liquid processes, such as gas dissolution, gas stripping and reactions between the gas phase and substances in the liquid phase will be improved.
As a consequence of a change in flow velocity of a gas liquid mixture crossing the velocity of sound in said mixture, gas bubbles in the liquid are very substantially broken up by the sonic shock wave created thereby. This phenomenon occurs upon an acceleration of the flow velocity of the gas-liquid mixture from a velocity of less than the speed of sound to one exceeding said speed of sound in the gas liquid mixture, and/or when the flow velocity is decreased from above to below said supersonic velocity. As a result of said shock wave effect, fine gas bubbles having diameters in the range of from about 0.1 to 0.01 mm are produced. For gas-liquid mixtures initially having larger sized gas bubbles typically having a bubble diameter of about 2 mm, the formation of such fine gas bubbles corresponds to an increase in bubble surface area on the order of 20 to 200 times compared to the surface area of the initial larger diameter bubbles.
The use of sonic shock waves to reduce the size of gas bubbles dispersed in a liquid is disclosed in the Garrett patent, U.S. Pat. No. 4,639,340, which is directed particularly to the dissolving of oxygen in waste water. Oxygen is introduced from a side pipe into a pressurized stream of waste water and is uniformly dispersed in said stream at a flow velocity less than the velocity of sound in the gas-liquid mixture. For this purpose, Garrett indicates that a flow velocity of at least about 2 meters per second should be used to establish a turbulent flow condition such as to create and maintain a uniform dispersion of gas bubbles in the liquid, apart from the oxygen that is dissolved in the waste water stream, immediately downstream of the point at which the side pipe for oxygen introduction joins the conduit through which the pressurized stream of waste water is being passed. Typically, such uniform dispersion of gas in liquid can be developed in a turbulent flow condition in a distance of at least about three times the diameter of the conduit. It will be appreciated, however, that the distance between the point of oxygen introduction and the positioning of means for acceleration of the gas-liquid mixture to supersonic velocity may be considerably longer than this distance in practical commercial applications. Garrett discloses the passage of the uniformly dispersed gas-liquid mixture formed at said velocity in the sub-sonic, but turbulent flow, range to a venturi for the acceleration of the flow velocity to a velocity in excess of the speed of sound in said gas-liquid mixture. Garrett states that, in the region of the venturi between its upstream end and its throat portion of minimum diameter, the velocity of said uniformly dispersed gas liquid mixture increases and reaches a velocity in excess of the velocity of sound in said dispersion, and that a sonic shock wave is created within said region of the venturi. As a result, the relatively coarse bubbles of oxygen in the dispersion are sheared into smaller or finer bubbles by the turbulence resulting from the shock wave. After passing through the throat of the venturi, the pressurized stream is deaccelerated as the venturi widens until it is returned to a sub-sonic velocity, which is nevertheless sufficiently high to maintain turbulent flow and the uniform dispersion of oxygen bubbles in the waste water stream. Garrett also discloses that, in the event the oxygen were introduced into the waste water stream through the throat of the venturi, as is conventionally accomplished for certain gas-liquid mixing operations, no sonic shock wave would be produced in the upstream, converging portion of the venturi.
Despite such advantageous use of venturi devices to enhance the dispersion of a gas in a liquid, there remains a desire and a need to further enhance the process and system for dispersing gases in liquids. Such requirements pertain to gas-liquid processing operations in general, and are related to the continual desire in the art for improvement in industrial processing operations. There is also a general desire in the art for a more efficient use of oxygen, nitrogen and other industrial gases in the wide variety of commercial applications in which industrial gases are presently employed or could be advantageously employed to improve the current practice in the art.
It is an object of the invention, therefore, to provide an improved process and system for the dispersion of gases in liquids.
It is another object of the invention to provide a process and system for enhancing the interfacial surface area between a gas and the liquid in which it is dispersed so as to enhance the mass transfer between said gas and liquid.
It is a further object of the invention to provide a process and system capable of enhancing the efficiency of gas liquid dispersion operations.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.